Abstract: A commercial yeast strain (L) and five yeast strains (Y-1, Y-2, Y-3, Y-4 and Y-5) isolated from different specialty sourdoughs were checked for their ability to metabolize sugars and organic acids and their effects on volatile flavor substances and sensory quality of sourdough and bread. The results showed that yeast Y-1, Y-3, Y-4 and Y-5 all showed good sugar metabolism ability and were able to produce high yields of malic acid, lactic acid and succinic acid. In terms of sensory quality, the sourdough fermented by each of the five yeast strains had good flavor; sourdoughs Y-3 and Y-4 had better sensory characteristics than other samples. It was found that the hardness of bread made with sourdough Y-3 was reduced by 16.77% and adhesiveness by 72.39% in comparison to commercial yeast L. The sensory score for fermented flavor of bread Y-3 was the highest, 7.74 points, indicating that yeast Y-3 could obviously improve the texture and flavor of bread. The results of headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) showed that the relative contents of alcohols in sourdoughs and breads made with L, Y-3 or Y-4 were the highest, ranging from 72% to 81%. Also, esters were the main flavor substances in sourdough, while aldehydes were predominant in bread. Moreover, the principal component analysis (PCA) of volatiles showed good discrimination among the three sourdoughs as well the three breads; ethyl hexanoate and ethyl caprylate contributed significantly to the flavor of sourdough Y-3, while hexanal and trans-2-nonenal were the key flavor components of bread Y-3. These substances provided rich aromas to sourdough and bread. In conclusion, yeast Y-3 plays a positive role in improving the taste quality of bread.

Key words: sourdough yeast; flavor substances; headspace solid-phase microextraction-gas chromatography-mass spectrometry; sensory evaluation